Vitamin D Flashcards
what form of vitamin D is cholecalciferol
Vitamin D3
What form of vitamin D is ergocalciferol
Vitamin D2
Vitamin D3 is synthesized where?
epidermis of the skin from UVB
Sources of Vitamin D3
fish, eggs, dairy, UVB
Sources of Vitamin D2
mushrooms, dairy
_____ absorbs UV photons producing provitamin D2
ergosterol
_____ has unstable bonds that rearrange with heat forming ergocalciferol
PREvitamin D2
where is provitamin d3 (7-dehydrocholesterol) synthesized
in the sebaceous glands of skin from cholesterol
what does provitamin d3 absorb
UV photons and is then converted to precalciferol (previtamin d3)
precalciferol has ____ bonds that rearrange in 2-3 days resulting in _____
precalciferol has UNSTABLE bonds that rearrange in 2-3 days resulting in CHOLECALCIFEROL
cholecalciferol diffuses from what?
skin, into blood
how is cholecalciferol transported to blood
by vitamin D binding protein DBP (transcalciferin)
dietary vitamin d in association with dietary fats in packaged into what? how?
into micelles with the aid of bile
vitamin d is absorbed how? where?
passive diffusion in the distal small intestine
vitamin d from the skin is transported how?
diffuses directly into the blood and id pick up by DBP for transport
where does vitamin d from the skin on the DBP travel
to the liver, but it can be picked up by other tissues (adipose, mm)
dietary vitamin d is incorporated into what for transport
chylomicrons within the enterocytes for transport
chyloomicron remnants deliver the vitamin D where?
liver
where else can the vitamin d in the chylomicrons be transferred to DBP for delivery?
to extrahepatic tissues
25-hydroxy vitamin D3 aka____
calcidiol
25-(OHD3) synthesized from vitamin d in the _____ by what?
25-(OHD3) synthesized from vitamin d in the liver by 25-hydroxylase
what cofactor is required for the synthesis of 25(OHD3) from vitamin d?
Mg
what is the main circulating form of vitamin d and most accurately reflects vitamin d levels
25-OHD3
1,25 dihydroxy vitamin d3 (1,25 (OH)2 D3) aka_____
calcitriol
where is 1,25 (OH)2 D3 synthesized and from what and via what enzyme
in the kidney, from 25-OHD3, 1-hydrozylase
which is the active form of vitamin D
1,25 (OH)2 D3
1,25 (OH)2 D3 OR 25-OHD3 functions as a steroid hormone
1,25 (OH)2 D3
vitamin d activity is regulated by_____
1-hydrozylase activity
1-hydroxylase is stimulated by
PTH
low plasma Ca
low 1,25 (OH)2 D3 [ ]
1-hydroxylase is inhibited by
high 1,25 (OH)2 D3 [ ]
high plasma Ca
high K intake
when 1,25 (OH)2 D3 levels are high, there is an increased conversion into _______ and conversion of 25-OHD3 into _______
when 1,25 (OH)2 D3 levels are high,there is an increased conversion into 1,24,25 (OH)3 and conversion of 25-OHD3 into 24,25 (OH)2
cholecalciferol is sotred mainly in the :
liver and adipose tissue
25-OH is store primarily in the
blood and muscle
vitamin d functions as:
steroid hormone
Vitamin d actions are mediated through what
VDR
inside the cell 1,25 (OH)2 + VDR bind to what
VDREs
1,25 (OH)2 + VDR + VDREs do what
initiate a cascade of molecular interaction that modulate the transcription of specific genes.
Vitamin D is essential for the efficient utilization of ______ in the body
calcium
Parathyroid gland secrets PTH when calcium levels are ____
low
PTH stimulates the activity of
1-hydroxylase in the kidney
PTH of 1-hydroxylase int he kidney results in
increase conversion of 25-OH to the active calcitriol
increased calcitriol production restores normal serum calcium levels in what 3 ways
- activation vitamin d transport system
- stimulating production and maturation of osteoclasts
- increasing the reabsorption of calcium in the distan renal tubules
PTH increases or decreases calcium mobilization
increases
the process of calcium homeostasis is controlled by
negative feedback loop - where increasing serum calcium and calcitriol levels inhibit PTH secretion and calcitriol production
______ is required for the differentiation of many cell types
calcitriol
calcitriol is required for the differentiation of WHAT cell types
skin epidermis
premyeloid WBCs, stem cells into macrophages and monocytes
stem cell monocytes in the bone marrow into mature osteoclasrs
calcitriol inhibits what cell type proliferation
fibroblasts, keratinocytes, lymphocytes
abnormal intestinal lymphatic, mammary and skeletal cells
true or false: calcitriol can induce cell apotosis
true
low vitamin d levels are associated with increasde risk of developing and dying from several cancers including
prostate breast colon ovarion non-hodgkins lymphoma
________ is a potent immune system modulator
1,25 OH2
VDR is expressed by most cells including
t cells, APCs
inadequate vitamin d levels are linked with what other diseases
RA, crohns, MS, DM 1
____ plays a role in insulin secretion
1,25 OH2
T or F, adequate Vitamin D levels are important for decreasing risk of high BP
true
Vitamin D metabolites are excreted in the
feces (70%) and urine
the amount of vitamin d produced in the skin depends on what
season level of latitude time of day degree of pigmentation age
in vitamin D deficiency ______ absorption cannot be increased enough to satisfy the bodys needs
calcium
when calcium absorption is not enough to satisfy the bodys needs _____ is increase and calcium is mobilized from the skeleton to maintain normal serum calcium levels
PTH
In children vitamin D deficiency is called
rickets
signs and sx of rickets
bone mineralization defects dental abnormalities growth retardation muscle weakness seizures
bone minerailzation defects in rickets result in
enlarged joints legs bow, knees knock spine becomes curved pelvic and thoracic deformities delayed closure of fontanels
in adults vitamin d deficiency is called
osteomalacia
signs and sx of osteomalacia
bone mineralization defects mm weakness low back pain/ aches fatigue sweating
increased risk of vitamin D deficiency in
insufficient sun exposure exclusively breast fed infants dark skin aging obesity fat malabsorption syndromes
people with dark coloured skin synthesize LESS OR MORE vitamin D than light colour skin
less
the elderly have a INCREASED OR REDUCED capacity to synthesize vitamin D when exposed to UVB
reduced
once vitamin d is synthesized in the skin or ingested, it is deposited _____
body fat stores
the vitamin D in body fat stores makes vitamin d LESS OR MORE bioavailable
less
vitamin D supplementation is clinically indicated for
osteoporosis
cancer prevention
the preferred form for supplementation is
cholecalciferol (D3)
hypervitaminosis D induces what
abnormally high serum calcium levels
abnormally high serum calcium levels could result in
kidney stones
calcification of soft tissues
certain medical conditions can increase the risk of hypercalcemia in response to vitamin D…..what are they
hyperparathyroidism sarcoidosis TB lymphoma * increased caution should be taken when supplementing these individuals
which is more toxic D2 or D3
D2
T OR F - excessive sun exposure is not associated with risk of vitamin d toxicity
true
signs and sx of hypervitaminosis D
hypercalcemia hypercalciuria loss appetite, constipation, n/v mm weakness hypertension and cardiac arrythmias calcification of soft tissues renal dysfxn mental confusion death
Vitamin D increased the intestinal absorption of what two minerals
Ca and P - promotes deposition into bone
what mineral is required for the conversion of vitamin d3 to 25(OH)D3
Mg
synthesis of what vitamin dependent proteins are stimulated by 1,25OH2
Vitamin K
what is the best indicator of vitamin d status
serum 25 (OH)
